[rules-users] Problem using 'not contains'

This is in Drools 4.0.7 I have a class called SatManager with a field: ArrayList<Satellite> listOfOverheadSats That has an appropriate getter method. I have a relatively simple rule that goes something like this: when $sat : Satellite(isOverhead == true) $sm : SatManager($ls : listOfOverheadSats not contains $sat) then $ls.add($sat); My problem is that Drools doesn't understand that the ArrayList has been modified, therefore this rule always fires on the same satellite if the sat object changes in any other way. I've tried adding: update($sm); To the consequence, but that only caused the rule to re-fire infinitely -- even with the no-loop keyword applied. So my question is how does Drools manage its knowledge of changes to Collections embedded in fact objects? The documention for the 'contains/not contains' keyword did not explain this. I'm really stumped here. Allen F. Bagwell e-mail: afbagwe(a)sandia.gov phone: 505/284-4517 fax: 505/ 844-7886 Ask your doctor if medical advice from a TV commercial is right for you.